e/Illustrations of the rule against perpetuities

Information
has gloss	eng: The fertile octogenarian and the unborn widow are two legal fictions from the law of real property (and trusts) that can be used either to invoke the rule against perpetuities to make an interest in property void or, alternatively and much more frequently, to demonstrate the seemingly bizarre results that can occur as a result of the rule. The rule itself, simply stated, makes a future interest in property void unless it can be logically proven that the interest must either vest or fail to vest within 21 years after the end of a life in being at the time the interest is created.
lexicalization	eng: Illustrations of the rule against perpetuities
instance of	c/Wills and trusts